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IDProjectCategoryView StatusDate SubmittedLast Update
0008568Open CASCADEOCCT:Visualizationpublic2005-04-08 16:122012-01-16 13:41
ReportersanAssigned To 
PrioritynormalSeveritytrivial 
Status closedResolutionfixed 
OSAll 
Fixed in Version5.2.3 
Summary0008568: Regression of transparency implementation as compared to OCC 3.1
DescriptionIt is clear from the two sample images attached that the current transparency
implementation is much worse than in version 3.1.

This problem appeared as a result of solving BUC60918 by GG.

However, it is obvious that the situation is much better, if we roll back GG's
modifications in OpenGl_attri.c.

After all, there is still a problem when several transparent objects are
displayed (they are always blended according to display order, not according to
their Z order for the current view angle) - it is beyond the scope of this bug,
have much higher complexity and should be treated separately.
Additional information
and documentation updates		Documentation remark, added by SAN 2005-04-19 14:41:20:

Changes:
Regression of transparency implementation as compared to OCC3.x was fixed.

However, transparency problem in general partially remains even for a single
transparent object. Undesirable visual effects can be seen resulting
from lighting calculations performed by OpenGL: calculated color of two
triangles A and B (one lying on a part of shape more distant from the eye,
another on a closer part, both oriented differently with repsect to light
direction) is different.
Therefore, result of blending "backround color -> 0.9 * A color -> 0.9 * B
color" is different from blending "backround color -> 0.9 * B color -> 0.9 * A
color". In other words, the resulting image still depends on order of triangles
in object's triangulation.

In order to avoid problems of different nature - wrong blending of opaque and
transparent objects (like an opaque object not
showing through a transparent one due to the latter being displayed first),
application developers should take care of displaying objects in proper order.
The easiest way to do this is demonstrated in AIS_Shape::Compute() method:
highest display priority (10) is forced for transparent objects, so that they
are drawn the last.
TagsNo tags attached.
Test case number

Attached Files

  • transparency_occ31.png (161,532 bytes)
  • transparency_occ52x.png (195,093 bytes)
  • transparency_vtk422.png (25,585 bytes)
  • ael-OCC8568-v1.tar.gz (10,860 bytes)
  • transparency_modified_occ52x.png (122,227 bytes)
  • transparency_0_1_bug.png (93,893 bytes)

Relationships

duplicate of 0002744 closedsan Open CASCADE transparency problem 
related to 0006268 closedael Open CASCADE Incorrect functioning of transparency 

Activities

2005-04-08 14:12

 

transparency_occ31.png (161,532 bytes)

2005-04-08 14:13

 

transparency_occ52x.png (195,093 bytes)

2005-04-08 14:52

 

transparency_vtk422.png (25,585 bytes)

san

2005-04-08 16:15

developer   ~0010114

*** Bug 2744 has been marked as a duplicate of this bug. ***

2005-04-15 11:56

 

ael-OCC8568-v1.tar.gz (10,860 bytes)

2005-04-15 12:22

 

transparency_modified_occ52x.png (122,227 bytes)

2005-04-19 12:40

 

transparency_0_1_bug.png (93,893 bytes)

Issue History

Date Modified Username Field Change
2005-04-08 16:15 san CC => enk
2005-04-08 16:23 san BugsThisDependsOn => 6145
2005-04-08 16:23 san CC =>
2005-04-08 16:33 vtn Assigned To bugmaster => san
2005-04-08 16:33 vtn Status new => assigned
2005-04-08 16:34 san Assigned To san => ael
2005-04-15 14:14 bugmaster CC => mkv
2005-04-15 14:18 bugmaster BugsThisDependsOn => 978
2005-04-15 14:20 bugmaster BugsThisDependsOn => 6268
2005-04-15 15:35 mkv CC => aki
2005-04-19 10:18 san Status assigned => resolved
2005-04-20 12:51 aki Status resolved => tested
2005-04-20 14:55 apv CC => apv
2005-04-25 10:15 bugmaster Status tested => verified
2005-05-06 15:35 bugmaster Status verified => closed
2005-05-06 15:35 bugmaster Resolution @0@ => fixed
2011-08-02 11:24 bugmaster Category OCCT:VIZ => OCCT:Visualization
2012-01-16 13:41 atp Assigned To ael =>
2012-01-16 13:41 atp Description Updated
2012-01-16 13:41 atp Additional Information Updated